Search

Abstract: An experimental study of the physico-chemical behavior of tungsten under severe conditions is presented. High temperatures (1300⩽ T ⩽2500K) generated by concentrated solar energy, high vacuum (∼10−6 hPa) and proton flux (1keV, ∼1017 ionsm−2 s−1) have been applied on polycrystalline W samples to simulate expected and also unexpected high heat loads that can occur on the ITER divertor (nominal and accidental conditions). During experiment, in situ measurements are performed and the material degradation, the mass loss kinetics, the characterization of the different species coming from the materials under coupled proton flux and high temperatures and the optical properties (reflectivity) are followed. Material characterization using SEM and XRD was investigated before and after treatment to understand the observed behavior. Bidirectional reflectivity measurements were carried out on the tested samples to explain the surface modifications, between the reference sample, the heated sample and the heated and ion irradiated one that can act on the thermo-radiative properties of tungsten. [Copyright &y& Elsevier]

Abstract: Heat load on spacecraft during atmospheric re-entry is of crucial importance, not only because of the thermal shield design and payload improvement, but also because of the threat that it represents for the passengers. One major part of the heat flux is due to the catalytic heterogeneous atoms recombination over the whole Thermal Protection System (TPS). As there is some evidence in the literature that the recombination coefficient of oxygen and nitrogen atoms is a key parameter to predict heat flux on TPS, the four major factors (temperature, pressure, nature of the material and recombination mechanism) that could affect the recombination efficiency are evaluated. Then, comparisons for different experimental and modeling results follow this part. Using two kind of silica surfaces, β-cristobalite and quartz, experimental results dealing with oxygen atoms recombination coefficient are discussed and compared with literature data and modeling. The various catalytic models found in the literature are helpful for a phenomenological understanding of the recombination process but usually too many parameters have to be adjusted by fitting with experimental results. Then, Molecular Dynamics simulation is more relevant to obtain accurate recombination coefficients. [Copyright &y& Elsevier]

In the framework of the H2020 European project POLYPHEM, whose main objective is to improve the flexibility and performance of small-scale solar power plants, studies have been conducted on various nickel-based alloys for the design of the solar receiver. Inconel 600 alloy is used as a reference material in the advanced manufacturing of high temperature solar receivers but other oxidation resistant alloys have been selected such as Inconel 617, Haynes 230, Haynes HR120 and Hastelloy X and the best candidate will be used for making the prototype. Thus, two essential quantities, namely the solar absorptivity α – the higher the better – and the total hemispherical emissivity ε – the lower the better – were measured in high vacuum and under atmospheric air up to 1400 K in the MEDIASE reactor installed at the focus of the 1000 kW solar furnace. The objective is to reach the best solar absorptivity and the α/ε ratio the highest as possible. The emissivity measurement was made by a direct method requiring the measurement of the true temperature of the material using a bi-chromatic pyro-reflectometer and that of its radiance by spectro-radiometry. Total hemispherical emissivity data are presented at the same time as microstructural (SEM, XRD) and topographic (3D profilometry) characterizations allowing the interpretation of the emissivity evolution with temperature and the growth of the oxide layer. Finally, the alloy Haynes 230 was chosen to build the solar receiver. • New original data of directional and hemispherical emissivity up to 1400 K for Ni-based superalloys. • Optical qualification at high temperature for Inconel 600 and 617, HX, H230 and HR120. • Detailed material characterization by SEM, XRD and 3D profilometry of the oxidized superalloys. [ABSTRACT FROM AUTHOR]

Highlights: [•] Inconel 625 alloy was exposed to plasma at high temperatures up to melting point. [•] Evolution of morphological and structural changes was determined by SEM, AES and XRD. [•] Depth profiling revealed different oxides on the surface depending on temperature. [•] Rich nano-structuring was observed but no nanowires appeared. [•] Hydrogen plasma treatment caused surface segregation of minor elements. [Copyright &y& Elsevier]

In this paper, the concentrated solar energy is used as a source of high temperatures to study the physical and chemical behaviors and intrinsic properties of refractory materials. The atmospheres surrounding the materials have to be simulated in experimental reactors to characterize the materials in real environments. Several application fields are concerned such as the aerospace and the energy fields: examples of results will be given for the heat shield of the Solar Probe Plus mission (NASA) for the SiC/SiC material that can be used as cladding materials for next nuclear reactor (gas-cooled fast reactor—GFR, Generation IV) and for new advanced materials for solar absorbers in concentration solar power (CSP) plant. Two different facilities—REHPTS and MEDIASE—implemented at the focus of two different solar furnaces of the PROMES-CNRS laboratory—5 kW and 1 MW—are presented together with some experimental results on the behavior of high temperature materials. [ABSTRACT FROM AUTHOR]

Abstract: A study on surface oxidation of AISI316L stainless steel surface was performed. Stainless steel was oxidized in air plasma with a high degree of dissociation of oxygen molecules of about 70%. The resultant flux of oxygen atoms to the surface was about 1×1024 m−2 s−1. The oxidation was performed at high temperatures ranging up to 1250K. The oxidation time was 5min. After oxidation the surface of the samples was analyzed by different methods including Auger electron depth profiling (AES), X-ray photoelectron spectroscopy (XPS), scanning electron spectroscopy (SEM) and X-ray diffraction (XRD). The microstructure and composition of the surface were temperature dependent. In all cases high Cr concentration was observed on the surface after oxidation at a temperature above 600K. With increasing temperature Mn concentration at the surface increased as well. Below 1000K the oxide film was uniform, while above 1000K islands with large spinel particles were observed to appear. [Copyright &y& Elsevier]